青光眼是一组威胁视神经视觉功能、与眼压升高密切相关的眼病。目前认为临床上大部分眼压的升高与房水流出阻力增加有关,特别是小梁网流出阻力的增加。因此,研究高眼压下影响房水外流阻力的重要区域-小梁网的形态学信息尤为重要。通过前房灌注的方法制造大鼠急性高眼压动物模型,将6只SD大鼠分成两组(A组和B组),B组大鼠处死后于左眼球加压60 mm Hg处理,其余眼球均为未加压对照组,利用双光子共聚焦成像系统采集正常眼压和高眼压下小梁网组织的断层序列图,通过图像处理方法,定量分析眼压对小梁网组织孔隙率变化的影响。通过三维重建获取正常眼压下的小梁网结构模型,并利用有限元方法,探讨眼压对于小梁网组织形态结构的影响。结合实验数据与模拟计算的结果,综合分析眼压的变化对于小梁网外流阻力的影响。高眼压组数据显示,部分小梁与周围组织融合,胶原纤维出现塌缩,越是靠近前房的小梁组织损伤越严重。有限元分析结果表明,孔隙越多的区域变形越大,而且压力越大,小梁变形程度越明显。眼内压升高可能会引起房水外流通道结构发生异常,主要表现为小梁网胶原纤维发生塌缩。高眼压与正常眼压情况相比,小梁网区域外流阻力增大的可能性较大。
As the aqueous humor leaves the eye, it first passes through the trabecular meshwork(TM). Increased flow resistance in this region causes elevation of intraocular pressure(IOP), which leads to the occurrence of glaucoma. To quantitatively evaluate the effect of high IOP on the configuration and hydraulic permeability of the TM, second harmonic generation(SHG) microscopy was used to image the microstructures of the TM and adjacent tissues in control(normal) and high IOP conditions. Enucleated rabbit eyes were perfused at a pressure of 60 mm Hg to achieve the high IOP. Through the anterior chamber of the eye, in situ images were obtained from different depths beneath the surface of the TM. Porosity and specific surface area of the TM in control and high IOP conditions were then calculated to estimate the effect of the high pressure on the permeability of tissue in different depths. We further photographed the histological sections of the TM and compared the in situ images. The following results were obtained in the control condition, where the region of depth was less than55 μm with crossed branching beams and large pores in the superficial TM. The deeper meshwork is a silk-like tissue with abundant fluorescence separating the small size of pores. The total thickness of pathway tissues composed of TM and juxtacanalicular(JCT) is more than 100 μm. After putting a high pressure on the inner wall of the eye, the TM region progressively collapses and decreases to be less than 40 μm. Fibers of the TM became dense, and the porosity at 34 μm in the high IOP condition is comparable to that at 105 μm in the control condition. As a consequent result, the permeability of the superficial TM decreases rapidly from 120 μm2to 49.6 μm2and that of deeper TM decreases from 1.66 μm2to0.57 μm2. Heterogeneity reflected by descent in permeability reduces from 12.4 μm of the control condition to 3.74 μm of the high IOP condition. The persistently high IOP makes the TM region collapse from its normal state, in which the collage
Elevated intraocular pressure appears to have a broader impact on increased resistance to aqueous humor outflow through the conventional aqueous outflow system(AOS).However,there is still no consensus about exact location of the increased outflow resistance of aqueous humor,and the mechanism is not perfect.In addition,it is difficult to accurately obtain hydrodynamic parameters of aqueous humor within the trabecular meshwork outflow pathways based on the current technology.In this paper,a two-way fluid-structure interaction simulation was performed to study the pressure difference and velocity in the superficial trabecular meshwork,juxtacanalicular meshwork(JCM)and Schlemm’s canal in response to JCM permeability changes.We obtained the JCM permeability of normal intraocular pressure varied between 1×10?15 m2 and 10×10?15 m2 while permeability of the JCM ranged from 2×10?16 m2 and 3×10?16 m2 under conditions of high intraocular pressure.The study indicated that the fluid dynamics parameters in trabecular meshwork and Schlemm’s canal are most significantly affected by the changes of JCM permeability.Moreover,the study demonstrates that the finite element modeling of AOS provides a practical means for studying the outflow dynamics and the biomechanical environment of the AOS.
